Posted
by
Soulskill
on Monday May 24, 2010 @05:31PM
from the wonder-if-it-will-rise-again dept.

coondoggie writes "NASA officially ended its Phoenix Mars Lander operation today after a new image of the machine showed severe ice damage to its solar panels, and repeated attempts to contact the spacecraft had failed. 'Apparent changes in the shadows cast by the lander are consistent with predictions of how Phoenix could be damaged by harsh winter conditions. It was anticipated that the weight of a carbon-dioxide ice buildup could bend or break the lander's solar panels. [Michael Mellon of the University of Colorado] calculated hundreds of pounds of ice probably coated the lander in mid-winter.'"

The plane passed approximately 6 metres (20 ft) above passing cars on the A30 and the airport's Southern Perimeter road. It also passed near a car which had just dropped off the Prime Minister of the United Kingdom, Gordon Brown.

A. It wasn't a rover.B. They knew that this would happen.C. The only reason they didn't use RTGs was because of cost and the nut cases that would protest the launch.

I know why they used solar. It was good enough for this mission.But it would have been really interesting if they where given the budget to use an RTG and had kept gathering data over the winter.So no knuckle head I was not criticizing their skills. Just lamenting that the mission was so limited in scope.

Of course, an RTG would mass much more than solar power so every part of the system would have to be beefed up. Launcher, cruise stage, aerobraking. Before you know it you are paying for two missions when one at that location was all you needed.

Which funnily enough is the concept behind the Mars Science Laboratory. A much bigger rover with a nice big RTG for power and heating. But we're only sending one.:)

Oh speaking of rovers, Spirit and Opportunity do have radioisotope heaters on them, but they wouldn't be enough to keep one alive through winter. I doubt they would have saved Phoenix if it was buried under that much ice.

Oh speaking of rovers, Spirit and Opportunity do have radioisotope heaters on them, but they wouldn't be enough to keep one alive through winter. I doubt they would have saved Phoenix if it was buried under that much ice.

If Phoenix was warm enough to sublimate all that CO2 away it might have not been able to investigate volatiles. It makes sense to send a big RTG heated rover now because this is a third generation vehicle, starting with Pathfinder. The risk of losing it during landing is smaller and the benefit a long traverse across the surface has been established.

I think the controlled drop method that they used on Phoenix proves that they can hold it stationary long enough, which is the great thing about the approach they've been taking. Each missing adds some capability; with MSL they'll be demonstrating they can land something large gently. Eventually we'll be up to habitats, and will have done great science along the way.

C. The only reason they didn't use RTGs was because of cost and the nut cases that would protest the launch.

Although I'm betting that cost alone was a sufficient driver of the decision. Why spend the extra money to use RTG when solar is all you need? I'm all in favor of using nuclear power when it's called for, but I'll never understand this "nuclear uber alles" viewpoint that some people seem to have.

Heavier yes.more complex? How? the RTG is a very simple device. Actually a lot less complex than the unfolding structure that the solar panels required not to mention the batteries and charging system. Plus I will bet they already included a radio isotope heater on the lander.The real reason they didn't use them is cost. It would have made the lander and launch vehicle more expensive. And yes for the mission requirements it would have added unneeded cost. It would have only made sense if the mission was mor

Your analysis is 100% correct assuming the REST OF THE MACHINE could function for years without any increase in complexity and weight. My guess is no. Yes a radio that operates "forever" costs about as much as a radio that operates for a couple weeks. I'm not completely familiar with the science instruments onboard, some things like magnetometers operate "forever" but some things like gas analysis systems complete with reagents and vacuum pumps and purge gases have a very finite life. Optics get covered

But at no time did you say that it would be less reliable. That was my main point. As I said for the scope of this mission solar was a good choice but it would have been interesting to get measurements of the the snow on the ground over winter and weather for the entire winter. At some point I am sure we will put another lander on the pole with an RTG for such a mission.

So, you've got a weight budget of 1 Kg for a tank for the helium for the gas analyzer, for three months. Not a serious engineering problem.

You bolt on the RTG and the mission now lasts 10 years. No problem man, all you need is 40 times the helium. Which you don't have the budget to lift. But helium is pretty light, and metal is pretty heavy. We'll make the total WAG that if you lightened the helium tank by 50% that tank mass could be replaced by

It would have had to be an awesome RTG to survive a Martian polar winter. CO2 ice forms below -100C and we believe the probe was covered in nearly a foot of this stuff. The coldest temperature measured was -97C, while the Phoenix was still running... You'd have to keep it warm, keep the ice from forming, and melt any "snow". That's a formidable task.

Isn't that what the "T" in RTG is for? Since you can't shutdown the decay, it's always warm and in winter you should get an extra few Watts since the temperature gradient is steeper. Just in case if you want to warm sth up (if you really have to).

... and you designed it to give a 150 degree delta V to survive the winter, in the summer she cooks along at perhaps 175 degrees C. A bit toasty. Yes I know there are heavy and complicated compressed gas / spring control arm systems and other such foolishness available, but they're heavy. Perhaps if we removed all the scientific instruments we'd have the weight budget to land a survivable multi-year infrastructure platform, but it would have nothing to do since all the instruments had to be removed.

I knew the T was "Thermal". The point you missed was the magnitude required. It's one thing to keep the probe warm. It's another entirely to melt the snow and ice and prevent any accumulation. There's a significant amount of heat that would be absorbed in liquifying or sublimating that ice.

Then, as another poster pointed out, what do you do with the heat in the summer? All that heat dissapation might affect the soil in the area around the probe; the soil that you're trying to study.

With an RTG you wouldn't need any solar cells. With out the solar cells they would not have been broken off by that accumulation of snow and ice.No need to melt all the snow off the probe. Just use the power to run heaters to keep the probe alive over winter and maybe some low rate data transmissions.

That's a good point. Phoenix ended up with, I believe, an estimated 7" to 8" of ice accumulated. The ice would have an insulating effect on the chassis. However, if you intended to maintain use of the arm, camera, or any externally mounted instruments, you'd need to supply their heaters. It is all possible, of course. You could put a 100kWe reactor on the pole and have it operate year round. It's a question of mass and budget. If you have funding them my argument falls on its face...

But, if the mass of the RTG's meant removing sensors in order to hit mass and volume budgets, there wouldn't have been any reason to care if it survived the winter. The MER's were done with basically the same launcher as Sojourner, so the fact that they accomplished as much as they did compared to Sojourner is truly amazing, IMO. Unfortunately, it's all about tradeoffs. Hopefully, Mars gets some serious attention and we can deploy some seri

I know all the reasons why they used solar cells. And it all comes down to cost.You are right that it was a great mission. I think too many people think I am being critical of the people that built and ran the mission. Not at all.I am just lamenting that it wasn't larger in scope.

Perhaps, but there's still the part where the whole rover gets covered in hundreds of pounds of dry ice. Maybe an RTG could have kept it from being buried, who knows.

If RTGs get your heart going, just wait for the Mars Science Lander [wikipedia.org], scheduled for next year's launch window. It's an RTG-powered rover that should last on the surface for quite a while. How long? After 10 years, the RTG should still provide 100 watts.

The two Viking landers were also nuke-powered, and Viking 1 lasted for some six Eart

Remember that the lander was not meant to last through the Martian winter, and in fact was only tasked with a three month long mission. It lasted five months, which was longer than expected. The newer rovers are supposed to be able to survive for much longer, but this mission accomplished all that it was supposed to.

Spirit and Opportunity, among other missions, have created an expectation that whatever we send out can last virtually forever. It's almost disappointing when these things are "only" completely successful, instead of wildly exceeding our imaginations.

Filming was set to begin on another James Cameron movie and they had to clear out the Mars studio. Failure of the lander was the plausible story concocted to allow for the timely cessation of the project.

The Illustrious Council of Elders has declared today a day of celebration. K'breel, Speaker for the Council, spake thus:

"Despite the propaganda reports to the contrary, what we killed a year ago remains dead and frozen, crushed beneath a mountain of toxic dihydrogen monoxide. The perverse pendulosity of its plumb bob [slashdot.org] waves no more!

Some say this war will end in fire, others in ice.
Reporters' gelsacs know my ire;
they are those who went with fire.

We now confirm this blue death twice,
Our gelsacs engorged with delight,
We say that for destruction ice,
Not only might,
But did, suffice!"

When the Martian Poet Laureate reported a striking similarity between the recent press release and an ancient transmission from the blue world, K'Breel had the Poet Laureate's gelsacs bobbed, frosted, and then bitten.

(and for the few and far that know not the original: i think it is exquisite also)

Some say the world will end in fire,Some say in ice.From what I've tasted of desireI hold with those who favor fire.But if it had to perish twice,I think I know enough of hateTo say that for destruction iceIs also greatAnd would suffice.

The solar panels provide power. You cannot provide more heating power than the sun does. The sun is putting energy into everything. Everything is still frozen. I hope you can work out the rest of the logic yourself.

I was not saying the panels power the defrosters directly. Let's say you use the batteries to heat up the panels, ice slides down, panels don't break and can recharge the batteries. I'm guessing that thing has batteries and was not running on solar power only.

(ie: use a couple of watts from the batteries and let them get recharged by the now de-iced panels)

First of all, ice doesn't slide down just because you heat what it's on. Due to the whole objects having a tip and ice building on them like a cap on someone's head. Of course once you got a meaningful amount of ice on the rover would probably be a hunk of dead metal due to lack of electricity and thus heating of electronics.

Second of all, you're gonna need a lot more than a couple watts to do anything. Likely many orders of magnitude more than what you'd get from the solar panels.

By your logic, there's no point having defrosting wires on Earth, either. Or indeed there's no point cooking with anything other than a solar stove.

The sun provides the energy, true, but its energy is spread and available for a limited time - the defrosting wires would provide heating in a specific place and the idea posed above would be to use stored energy to extend the life.

Other practical considerations may have gotten in the way, but your logic is faulty.

Sigh, honestly. I give people the benefit of the doubt in terms of logical thinking and this is the replies I get.

Mars!=Earth. If we had a magical energy storage device we could have the lander run at full power 24/7 without any problems. Clearly we don't in this one, I figured it went without saying. Batteries are very much short term. A RTG would work but the rover doesn't have one and the question was limited to the current situation.

It's all practical questions in these sorts of cases. Saying "in a magi

I was taking issue at the argument that "you cannot provide more heating power than the sun does", because I would say that it's clearly possible to do so, as long as you're talking about a specific and limited heating. You are of course right in saying that heating would require an energy source, but you're also using a model whereby the batteries aren't taken into account, because you dismiss them as short term - it's not like Spirit and Opportunity's batteries haven't held out for this many years.

First of all, let's ignore the fact that the probe does not generate enough power during winter even without any ice for minimal heating much less storing anything. That pretty much kills your proposal.

Second of all, all operations cannot be shut off. Mars is cold. The sort of cold that is outside the safe temperature zone for even specially designed electronics and batteries. So you've got a constant power drain or your chance of anything working after winter are very low. Which as I said is in practice mo

The sun was down too far on the horizon to generate any useful power (or absorb heat directly) during winter.

Mars has axial tilt of 25 degrees; Earth's is 23.5 degrees or so. So there's an equivalent Arctic Circle zone where the sun's below the horizon during the worst of winter. Earth's Arctic Circle is at 66 degrees north; with slightly greater tilt, Mars' Arctic Circle will be even lower. The landing site was around 67 degrees north on Mars.

The sun would have been down long enough that no reasonable amount of batteries could have kept it warm overwinter. A RTG could - as discussed - or little RHU units (Radioactive Heater Unit - it's like a mini-RTG heat source module, with the protection but no power generation units, just designed to keep parts warm). But there was a decision made that the lander was unlikely to survive with all the overwinter issues, so they didn't bother.

It's fascinating to watch NASA begin to really explore a place like Mars that has a dynamic environment. The Moon is mostly changeless (except for Earth's shadow periodically swinging by, and the occasional tiny meteorite). Planetary orbits are dynamic at only the subatomic (eg. solar wind) scale, except for the rare encounter with space junk. But Mars is a real planet, with weather and lots of energetic events lots of the time.

It's not just far away that makes it hard. It's being so close to the Earth in having a dynamic atmosphere and possibly even surface conditions that makes it hard.

And that is why we do it: not because it's easy, but because it's hard. Doing it makes us better, and shows how good we are. Go NASA!

Hopefully they will learn from this, in hopes that the next gen of these rovers have the capability to set themselves up for a shutdownwith minimal damage or the possibility for a wake up from a dormant state, i am not sure if winter has passed, but now the ice has melted and the sun is shining on those panels...it would have been great to have it wake up and start all over again.....!

Probably not, unless it's in very small quantities. Atmospheric concentration is pretty low, and either way, at 1 bar it doesn't freeze until about -78C. I don't think there are any natural places on Earth that cold.

Yes there is. Those temperatures have been observed on the south pole. (Read a report about a team that did stay “overnight” [= over winter]) And that doesn’t even include the windchill effect. Which can make it feel like a horrible -140C. A temperature that literally smacks you in the face so hard you fall over backwards. A temperature that lets your breath crackle and freeze before it lands on the floor. A temperature where pissing in the snow may make you impotent trough freezing the inside of your penis all the way.Yes, there you might find some dry ice... (e.g. the one that you just did breath out.)But good luck finding it in nothing but endless planes of real actual ice.;)

Wind velocity has no effect on actual temperature. Wind chill was originally meant to indicate how long it will take your skin to freeze in sub-freezing temps. It's supposed to be a time measurement, not temperature.

The windchill effect is basically a made up term that is _supposed_ to tell you how likely the surrounding atmosphere is to give you frostbite, though no one can agree on a decent standard that works well. It is pointless trying to apply it to freezing rates of any substance (notice how ice (basically) always freezes at 0, whatever the windchill?).

Ok, I just found a page with waaaaaaaaay too much information [wattsupwiththat.com], but I'll give you the short brief. First by the lower pressure at the poles and higher elevation of the coldest measurement stations, you might not pass the freezing point at all, it seems right on the border. Secondly, because there's so little CO2 in our athmosphere the sublimation effect is much stronger than the freezing effect, dry ice won't last even if held below the freezing point.

because there's so little CO2 in our athmosphere the sublimation effect is much stronger than the freezing effect, dry ice won't last even if held below the freezing point.

What do you mean by that? In order for a phase transition to occur, there has to be some change, either in temperature, pressure or concentration. If the conditions are such that a solid CO2 phase is dictated, you can be sure that it will "last"...

The vapor pressure of 'dry' CO2 ice is larger than the partial fraction of gaseous CO2 in our atmosphere. That means that it will sublimate, even if it's below the freezing point. You have to go far below the freezing point, until you find the temperature where the vapor pressure is lower than the partial fraction.

This is why water ice will sublimate in very cold, very dry air. If the humidity is low enough, a blanket of snow will slowly disappear, even at -20 C. You can see that in the Midwest every winter.

The other problem I imagine you'd have is that the CO2 in the atmosphere is moving. Those very cold parts of the earth tend to also be very windy, and like how a flowing river can see temperatures below 0C and not freeze, I would imagine CO2 would have a hard time freezing out of the atmosphere while blowing around at high speeds.

I don't know offhand; but, looking at its phase diagram [wikipedia.org], it struck me that there is probably some lurking somewhere dark and cold in the very deep ocean, or possibly at a few PPM among the normal snow in the coldest terrestrial regions. I know of nowhere where it has ever been observed in any quantity, outside of manufactured environments.

Maybe, lurking somewhere, but probably not. The bigger issue is saturation levels. Solid CO2 at the ocean depths would be far higher in "CO2'" than the ocean water. Thus, it would be entirely soluble, and would be absorbed by the seawater.

Solid CO2 is far, FAR higher in CO2 than any air or water around. Due to that, it would quickly sublime or dissolve. There's really nowhere on earth you could find naturally occurring dry ice.

Actually, it makes as much sense as frozen water as "ice". Anyone who thinks otherwise is simply not as fluent in the English language as they could be. Someone who isn't as familiar with the language is likely to try to puzzle out nonexistent rules because they aren't familiar with the linguistic conventions that apply in the case at hand. But those who are familiar with how the language is used know that "ice" is a word that applies to certain cases of solids without regard to their chemical compositio

I cannot think of any time anyone would use the word ice (alone without adjectives) to mean anything else, save for completely unrelated slang. Educate me....

I can't think of any situation on Earth where "ice" would be used to mean anything but water ice, since everything else requires such otherworldly conditions. NASA scientists are a bunch of space cadets. Speak English not Martian!

Hintedy hint.:)

But seriously, it's not like they didn't specify at any point in the article that they meant CO2 ice. If